ABSTRACT
Inefficient coal combustion is a significant source of elemental carbon (EC) air pollution in China, but there is a limited understanding of EC's formation processes. In this study, high time-resolved particle number size distributions (PNSDs) and size-resolved chemical compositions were obtained from the combustion of four bituminous coals burned in a quartz tube furnace at 500 and 800 °C. Based on the distinct characteristics of PNSD, the flaming stage was divided into the first-flaming stage (with a PNSD peak at 0.3-0.4 µm) and the second-flaming stage (with a PNSD peak at 0.1-0.15 µm). For the size-segregated EC and OC measurements, more soot-EC was observed in particles larger than 0.3 µm, whereas the smaller ones possessed more char-EC. The results indicated that gas-phase and direct-conversion EC generation mechanisms dominate different burning stages. The analysis of 16 parent PAHs showed more high-molecular-weight PAHs in the second-flaming stage particles, which supports the idea of different formation processes for char-EC and soot-EC. For all four coals, the PNSD and chemical compositions shared a similar trend, confirming that the different formation processes of EC in different flaming stages were common. This study provides novel information concerning EC formation.
Subject(s)
Air Pollutants , Coal , Biomass , Carbon , China , Particle Size , Particulate MatterABSTRACT
Genus Oenothera includes medicinal plants that are distributed throughout the world and are known since ancient times.Popular indications of different species of this genus include treatment of inflammations,diabetes,microbial infections,ulcers,tumors,kidney and liver problems.The plants of this genus are a botanical source for various pharmaceutically active components like sterols,alkaloids,phenolic acids,flavonoids,tdterpenoids,saponins,bitlavonols and tocopherols.This review article is a compilation of chemical composition and biological activities of the various species of the genus Oenothera.
